just found a new exciting way for cheapest prepaid mobile calls within Austria and to the rest of the world:

Buy a T-Mobile Klax Prepaid SIM (€14,90, special offers also €6,90), activate tariff option My Faves (= my 5 favorite numbers to all networks, charged with 1ct/min).
There is an additional basic fee of € 1.- per month for this tariff.
It can be stopped by sending a SMS "stop faves" to 0676-2222

Register a Betamax access number as one of these 5 numbers, i.e. 012323232 for dialnow.com